The number 21165
21165 is a composite number with 16 divisors. Its prime factorisation is 3 × 5 × 17 × 83. Divisors (16): 1, 3, 5, 15, 17, 51, 83, 85, 249, 255, 415, 1245, 1411, 4233, 7055, 21165.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21165: a Harshad number: divisible by its digit sum 15.
- 2
21165 is composite. Its prime factorisation is
- 3
The divisors add up to 36288; without 21165 itself that is 15123, so 21165 is deficient (15123 is less than 21165). Euler's totient φ(21165) = 10496 numbers up to 21165 share no factor with it.
- 4
The digits of 21165 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21165 = 3 \times 5 \times 17 \times 83 \]
21165 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 36288 |
| Euler totient φ(n) | 10496 |
| Square | 447957225 |
| Cube | 9481014667125 |
| Square root | 145.481958 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1165 × |
21165 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and sixty-five |
| Binary (base 2) | 101001010101101 |
| Octal (base 8) | 51255 |
| Hexadecimal (base 16) | 52AD |
| Base 3 | 1002000220 |
| As time | 21165 seconds = 5 h 52 min 45 s |
Is 21165 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21165 ÷ 3 = 7055) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21165 ÷ 5 = 4233) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21165 a prime number?
No. 21165 = 3 × 5 × 17 × 83, so it is divisible by 3.
What are the factors of 21165?
1, 3, 5, 15, 17, 51, 83, 85, 249, 255, 415, 1245, 1411, 4233, 7055, 21165.
What is 21165 in binary?
101001010101101 (hexadecimal 52AD, octal 51255).
What is the square root of 21165?
About 145.4820.
Is 21165 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21165?
21165 is a Harshad number: divisible by its digit sum 15.